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Many of you have felt comforted by having a cellular phone handy in a tense situation, or a real emergency. Perhaps it was walking alone down a dark, deserted, downtown street. Or perhaps having to stop your car on a dark, deserted highway. Whatever, it was dark, and you were alone except for your cellphone that could always connect you to someone by dialing 9-1-1 (even if you had forgot to pay last month’s bill). However, life is not that simple. Assuming that you have coverage and that the digits 9-1-1 are accepted (surprisingly, it is still far from universal) and you are successfully routed to an emergency worker who is not too far away, the similarity with dialing 9-1-1 from a payphone or your house phone abruptly ends.
If you dialed 9-1-1 from a payphone, the emergency workers would immediately know your location and, if necessary, could ring you back to obtain more information (assuming that you hang around the phone). With a cellular phone, neither are possible. However, the TIA is nearly finished with a standard to enable these enhanced 9-1-1 features – to be gradually added to cellular (and PCS systems). TIA standards subcommittees TR-45 and TR-46 (which together are responsible for both AMPS and GSM-based standards) have formed a joint group to develop protocols to allow both an approximate location to be determined and the cellular phone to be called back. The development of this standard was a long process, with several steps:
The TIA is proceeding with a development in two phases that supports the joint agreement between the CTIA and emergency services organizations. If the FCC rule-making stands (and it is currently being vigorously objected to by carriers), some major modifications may have to be made, depending on the interpretation of some of the rather vague wording used by the FCC.
The first phase of standards development is almost complete and supports approximate location identification (i.e. the cell or sector of the caller), callback and automatic reconnect. The second phase of the standards development will address the provision of more accurate location information.
Phase I location information will be provided in the form of a telephone number, one of which must be allocated for each cell or sector in every wireless system. Callback will also be facilitated by providing a telephone number; the subscriber’s directory number. Therein lies a problem; the current signaling protocol used to connect to emergency services systems (known as CAMA) only supports one digit field. Consequently, emergency services systems will have to be upgraded to accept Feature Group D signaling (although an intermediate ‘black box’ could do the conversion transparently to both the wireless and emergency systems).
Assuming this information can be transmitted, a temporary ALI (Automatic Location Identification) record can be created, similar to the permanent records created for each landline subscriber. This record will contain the name and location of the cellsite (based on a lookup of the cell/sector phone number) and the directory number of the mobile.
Callback is accomplished simply by having emergency workers dial the mobile’s directory number stored in the ALI record, although there is a wrinkle here also, based on the subtle, but important, distinction between a MIN and a directory number. Most cellular phones (but far from all) have the 10-digit MIN programmed to be the same as the directory number. For phones that have a different MIN (e.g. many ‘shrink-wrapped’ and special-purpose phones) and that are roaming, the MIN is the only number available to the serving wireless system (at least until IS-41 Revision C is widely available). In this case, the emergency system would have to use the roamer port method to callback the mobile.
Another wrinkle with callback occurs when an inter-system handoff occurs and the user dials 9-1-1 while in a call. In this case, the cell or sector location will be passed back in an existing IS-41 message to the anchor system (where the call first started) and the emergency call will be set up there, using the cell/sector location digits from the neighboring system. Apart from this, and a restriction on dropping the 9-1-1 call leg, the call be will handled similarly to a regular three-way call.
Automatic reconnect is slightly different than callback, and requires no action by the emergency call taker. If a mobile disconnects abnormally during an emergency call, the wireless system will re-page the mobile in the cell it was last in, and possibly neighboring cells. If the mobile responds to the page, and the caller answers the phone, the call will continue. During re-paging, a tone or announcement will be played to the emergency system.
Automatic reconnect has a wrinkle related to inter-system handoff, just like callback. The serving system will have to be told by the anchor system that it is processing an emergency call, in order to know that reconnect must be attempted in the case of an abnormal disconnect (now do you understand why standards take so long to develop!).
The TIA standard for enhanced wireless emergency services is being developed under project number PN-3581 for both AMPS-based and GSM-based cellular and PCS standards. It may be published initially as a stand-alone document, but eventually will entail modifications to IS-41 (soon to be TIA/EIA-689) for AMPS inter-system operations, IS-93 for PSTN interconnect (e.g. Feature Group D signaling) and IS-651 for GSM inter-system operations.
For those that read only the first paragraph and skipped down to the conclusion (and I don’t blame you)...imagine it is a dark and stormy night in 1998 and you are walking down a lonely road when a gang of thugs swinging baseball bats comes round the corner. You dial 9-1-1, but just as the call is answered, you drop your phone and the battery pops off. You fumble the battery back in and the phone rings...“Will that be police, fire or ambulance? ... and what part of Wrigley Field are you in?”.
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